1. Field of the Invention
The present invention relates to a link type variable stroke engine, and especially relates to a link type variable stroke engine in which a crankshaft and a rotary shaft are each rotatably supported on a case main body and a support plate, the case main body formed integrally with a cylinder block and opened at one side to form a part of a crankcase, the support plate fastened to an opened end of the case main body at a plurality of positions, the rotary shaft having an axis parallel with the crankshaft and being provided with an eccentric shaft at an eccentric position, a piston slidably fitted to the cylinder block, the crankshaft and the eccentric shaft are linked by a linking mechanism, and the linking mechanism includes: a main connecting rod coupled, at one end, with the piston; a sub connecting rod rotatably coupled with a crank pin of the crankshaft and rotatably coupled with the other end of the main connecting rod; and a swing rod rotatably coupled, at one end, with the sub connecting rod at a position displaced from a position coupled with the main connecting rod and rotatably coupled, at the other end, with the eccentric shaft.
2. Description of the Related Art
In conventional reciprocating engines, explosion load is only applied between a cylinder head and a crankshaft. For this reason, such a reciprocating engine does not have any functional problem as long as coupling rigidity and strength between the cylinder head and the crankshaft are secured. Accordingly, as seen in many motorcycle engines and general purpose engines, for a configuration in which a crankcase includes a case main body integrally formed with a cylinder block and opened at one side, and a side cover fastened to the opened end of the case main body, and in which the crankshaft is rotatably supported by the case main body and the side cover, it is not necessary to take into account any directional properties, except for the above, in terms of fastening positions at which the side cover is to be fastened to the case main body. Thus, the fastening positions can be any positions as long as being provided at substantially regular intervals to prevent oil leak from coupled parts of the case main body and the side cover.
Meanwhile, a link type variable stroke engine has already been known by Japanese Utility Model Publication No. 57-32267, Japanese Patent Application Laid-open No. 9-228858, the specification of U.S. Pat. No. 4,517,931, Japanese Patent Application Laid-open No. 2002-285877 and the like. In the link type variable stroke engine, a piston, a crankshaft and an eccentric shaft are linked by a linking mechanism, the eccentric shaft provided to a rotary shaft which is parallel with the crankshaft and to which power reduced at a speed reduction ratio of 1/2 from the crankshaft is transmitted. At the time where explosion load occurs in such a link type variable stroke engine, in addition to the explosion load, internal load (components of force) occurs between mutual links, especially, between the crankshaft and the rotary shaft.
When explosion load occurs in the link type variable stroke engine, the explosion load is applied only between the cylinder head and the crankshaft as described above, and, at the same time, internal load (components of force) occurs between the crankshaft and the rotary shaft. However, none of Japanese Utility Model Publication No. 57-32267, Japanese Patent Application Laid-open No. 9-228858, the specification of U.S. Pat. No. 4,517,931 nor Japanese Patent Application Laid-open No. 2002-285877 discloses any support structure of a linking mechanism capable of handling such internal load.
If the rigidity between the crankshaft and the rotary shaft is insufficient and the distance between the shafts changes due to the internal load (components of force), the following problems (1) to (4) arise.
(1) The geometry of the linking mechanism changes and desired piston movement cannot be obtained, resulting in a compression ratio and an expansion ratio different from designed values. (2) The linking mechanism becomes misaligned due to excessive distortion and partial contact and partial wear occur at bearing portions, consequently increasing friction. (3) In a structure in which a gear mechanism is provided between the crankshaft and the rotary shaft, a backlash becomes smaller, causing friction noise and wear of tooth tips and bottoms. (4) In a structure in which a transmission mechanism using an endless belt or chain is provided between the crankshaft and the rotary shaft, the belt deteriorates, and occurrence of tooth-skipping and chain drive noise increase, when the belt or the chain loosens or has excessive tension.